Microfluidic devices have been widely used for receiving, processing and analysing biological cells/beads. The size of the channels in these devices, typically 1-1000 microns in diameter, allows accurate manipulation and control of individual cells.
An example prior art setup for processing and analysing biological cells/beads is shown in FIG. 1.
Prior to use, cells/beads are typically held in a suspension which is located in a reservoir. To prevent the cells/beads from this suspension from settling whilst in the reservoir, there is the need to ensure that the suspension is constantly stirred. To prevent such settling, a ‘bar’ stirrer is located at the base of the reservoir, which can rotate to keep the contents of the reservoir stirred.
The cell/bead suspension can be pumped out of the reservoir by applying pressured gas into the top of the reservoir. From the reservoir, the suspension is pumped into a tube which leads to a microchannel located in a microfluidic device. Inside the microfluidic device, the suspension is passed through the microchannel to a mixing point.
At the mixing point, the suspension is mixed with a further fluid(s), such as a different bead/cell suspension, and/or an oil-based fluid. Each further fluid is similarly pumped to the mixing point in the microfluidic device from a respective reservoir/tube/microchannel arrangement.
Downstream of the mixing point, the microchannel inside the microfluidic device delivers the mixed fluids to an output tube located off the microfluidic device. This tube then leads to an output reservoir where the mixed fluids are stored. The output reservoir is also located off the microfluidic device.
One disadvantage of the above setup is the use of the ‘bar’ stirrer which rotates at the base of the cell/bead suspension reservoir. This rotation causes damage to the cells located between the reservoir and the rotating tar′ stirrer, due to cells getting caught between the two surfaces, and also due to high shear forces in this region.
Since cells/beads tend not stay in suspension for long, and tend to settle out (due to differences in density between the cells/beads and the aqueous medium in which they are suspended), a further disadvantage of the above setup is that clogging, and thus blockages, tends to occur in the tubes and connectors between the reservoirs and the microfluidic device.
The present invention seeks to solve the above mentioned problems, and others.